Milling plant for sifting damp material



Aug. 18, 1970 H. JAGER v 3,524,544

MILLING PLAN? FOR SIF'I'ING DAMP MATERIAL Filed Aug. 20, 1968 l/WENIOR HEM/z Zeke/e United States Patent 3,524,544 MILLING PLANT FOR SIFTING DAMP MATERIAL Heinz Jager, Bochum, Germany, assignor to Westfalia Dinnedahl Groppel AG, Bochum, Germany, a German corporation Filed Aug. 20, 1968, Ser. No. 753,958 Claims priority, application Germany, Aug. 21, 1967, 1,607,623 Int. Cl. B07b 4/04, 7/83 US. Cl. 209-11 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The present invention relates to a milling or grinding plant for processing and separating pulverulent damp materials such as, for example, limestone and the like. Milling and crushing plants are known wherein the milled products delivered by a crusher and by a fine, precision grinding mill, for coarse and fine products, respectively, are supplied to a sitter or separator apparatus wherein the coarse pieces remaining on the sitter screen are returned to the grinding or crushing mill. In order to achieve a certain drying effect during this process, hot gases are supplied to the crusher and to the sifter or separator. In such known milling plants, which are also sometimes referred to as bucket-conveyor rotating mills, the milled or ground products of the crusher and of the fine mill are customarily fed into the same bucket-conveyor which delivers material transported in the buckets to. the sifter. However, when the raw material being handled has a high moisture content, the effectiveness of the sifter screen is greatly impaired due to the short period of time which the damp material spends in the sifter apparatus, and hence the equally short time available for drying out the moist material. Moreover, the dry fine material adheres to the moist crushed raw material and presents a problem which heretofore has required extra drying and extra handling through driers of both coarse and fine material.

SUMMARY OF THE INVENTION The present invention eliminates the above shortcomings of the prior art and aims to provide apparatus whereby the milled products of the crusher and of the fine mill are delivered separately to the sifter apparatus. The dry product coming from the fine mill is supplied to a centrifugal rotating scattering plate located in the upper portion of the sifter apparatus. On the other hand, moist material coming from the crusher, which is somewhat coarser in nature, passes into a hot region, heated by hot gases and located in the lower portion of the sifter apparatus. In this manner, the damp or moist material from the crusher cannot impair the efiiciency of the sitting process and size separation which takes place in processing of the dry rotating material coming from the fine mill.

Preferably, the sifter apparatus is constructed as a plurality of separate scattering plates located superimice posed, one above another and at a distance from each each other, each of two plates carrying out a different function.-Depending upon the particular conditions prevailing as to moisture content and grain size, and to adjust the desired scattering effect of the two plates in accordance with such prevailing conditions, it is preferable to provide each of the scattering plates with a variable speed drive. u

According to a modification of the invention, the sifter can also be provided with sitting or distributing devices of different shapes, for example a conical or trickling type of sitting apparatus. A centrifugal scattering device or a device which allows the material to fall through the air slowly will also accomplish the desired purpose.

The above-mentioned objects, advantages and features of the invention, set forth with particularly in the claims annexed hereto, will be apparent from the embodiments of the invention illustrated schematically in the following drawing shown by way of example and described hereinafter.

The figure shown in the drawing is a schematic cross sectional view in elevation of the apparatus according to the invention.

As shown in the drawing, the sitter apparatus of the invention is comprised of a first or upper sifter housing 1 which encloses a sitting chamber 1. Circulating sifting air, which entrains and thus assists in the separation of materials of various degrees of fineness, is supplied to the apparatus from a blower or ventilator fan 2, located on the outside of the housing 1. The circulating air moves upwardly through the chambers 1' and 4 in a circulatory cycle, entering the lower or distributing chamber 4 from the side thereof at 40 through the pressure outlet duct 3 on the outlet side of the blower fan 2. The circulating air enters the blower 2 through the suction inlet line 7 from the tops of cyclone separators 6 and 6a.

The circulating sifting or entraining air from blower 2, entering the lower chamber 4 from duct 3, flows along paths indicated by arrows 22, 24, 26, 28, through the individual superimposed comically-shaped separating sifter screens 30, 32, 34, 36, wherein hot air or gases, from source A dries the moist material. The circulating entraining air passes upwardly from the distributing chamber 4, through upper sifting chamber 1' and out of the sifter housing 1 into nipples or ducts 5 and 511, respectively, tangentially attached to the top of and leading into precipitating dust-collecting cyclones 6 and 6a in which the fine airborne material is precipitated and collected at pendulum-weighted receiving gates at 17 and 17a, respectively, located at the bottoms of the cyclone separators 6 and 6a, respectively.

Within the upper or first sifting chamber 1' is located a rotary or centrifugal scattering plate 8, driven in a rotary path from a shaft 9 above the scattering plate 8, the shaft in turn being driven by a motor 11 through a coupling and gear box 10.

The charged dry pulverulent material enters chamber 1' through a hopper (not shown) at 12 into a feed pipe or chute from which it drops on to the scattering plate 8 as the latter rotates,. The inlet pipe connection at 12 supplies the scattering plate 8 with relatively dry fine pulverulent material.

Below this upper scattering plate 8, which scatters the fine material, is located a second scattering plate 13, dis posed within the lower or distributing chamber 4 and supplied with damp moist coarser material which is fed in from the crusher through another hopper (not shown) by means of a feed pipe 14. As the first scattering plate 8 rotates, material which flows from it in a centrifugal path drops onto the sloping conical sides of the sifting chamber 1. Hot gases are introduced laterally into the lower distribution or classifying chamber 4 from a source A of hot gases or hot air through a hot inlet pipe 15, preferably in a tangential direction relative to chamber 4. Exhaust gases exit from the sifter apparatus in the direction of arrow C through the exhaust gas outlet pipe 16 which is connected to the upper portion of the pressure duct 3 of the blower 2.

Operation of the sifter apparatus of the invention is as follows: The dry pulverulent material, charged into the apparatus at 12, is thrown outwardly centrifugally by the rotating scattering plate 8 into the open space 1 of the upper sifting chamber 1. Heavier and coarser particles drop down as shown at 42 for classification, sitting and sizing in lower chamber 4. The fine material is airborne by the circulating sifter air and classified into coarser and finer grained material. The finer material is airborne and follows the combined arrows 38 through ducts 5 and 5a and are precipitated out in the cyclone separators 6 and 6a from which the material drops down into pendulum weighted type discharge chutes or traps.

The damp or moist material, charged separately at the chute 14, drops onto the second rotary scattering plate 13. The scattering plate 13 discharges its moist material into the heated chamber 4 onto the conically shaped separators or trickle-type sifter devices. The scattering plate 13 may rotate either at its own individual revolving r.p.m. speed, independently or at the same r.p.m. as plate 8. The arrangement shown in FIG. 1 illustrates a drive shaft 44 separate but coaxial with shaft 9. The scattering plate 13 is located within the distribution or classifying chamber 4 of the sifter apparatus. This arrangement permits a relatively long and intensive drying of the damp conveyed material entering at 14 to take place. The damp material from charging chute 14 falls onto rotating scattering plate 13 directly in the path of the hot gases which enter into the distribution chamber 4 at duct 15 in the direction of arrow A. The exhaust gases leaving the apparatus exist at 16 in the direction of arrow C through a dust filter (not shown).

It will be obvious to those skilled in the art, upon reading this disclosure, that modifications and alterations of this invention are possible, within the scope of the described invention and without departing from the essence thereof as set forth in the appended claims.

What is claimed is:

1. In an apparatus for size-classification of charged coarse and relatively fine raw materials such as limestone and the like wherein at least some of said materials are moist as charged into the apparatus, the combination comprising a housing, first sifter means arranged in the upper portion of said housing for receiving and size-separation of relatively fine charged materials, second sifter means within said housing spaced below said first sifter means and arranged for receiving and size-separation of relatively coarse charged materials including said moist materials, feeding means arranged to feed separately the relatively fine materials to said first sifter means, and to feed separately said relatively coarse and said moist materials to said second sifter means, blower means located outside of said housing and communicating therewith, a source of hot gases connected to the lower portion of said housing for heating and drying the moist materials, and collecting means arranged in the lower portion of said housing for receiving dried materials from said second sifter means.

2. Apparatus according to claim 1, said first sifter means comprising a first scattering plate having a surface mounted for rotation in a generally horizontal plane so as to centrifugally eject materials outwardly therefrom, airclassifying means arranged for receiving materials centrifugally thrown from said first scattering plate, duct means extending from said air-classifying means to said blower and from said blower to said housing to thereby define a circulatory path.

3. Apparatus according to claim 2, said second sifter means comprising a second scattering plate having a surface mounted for rotation in a generally horizontal plane so as to centrifugal eject coarse and moist materials outwardly therefrom, and drive means for rotating said first and said second scattering plates.

4. Apparatus according to claim 3, said drive means including means for individually varying the rotational speed of said first and said second scattering plates respectively.

5. Apparatus according to claim 1, said sifter means comprising a plurality of vertically coaxial-conical surfaces mutually superimposed and arranged for causing gravity trickling of the materials.

References Cited UNITED STATES PATENTS 1,746,686 2/ 1930 Sturtevant. 2,199,015 4/1940 Toensfeldt 20911 2,658,615 11/ 1953 Ebersole 209-11 2,956,347 10/1960 Gordon 209-11 FOREIGN PATENTS 70,084 4/ 1915 Austria.

TIM R. MILES, Primary Examiner US. Cl. X.R. 209139 

